#include<iostream>
using namespace std;
  struct ListNode {
      int val;
      ListNode *next;
      ListNode() : val(0), next(nullptr) {}
      ListNode(int x) : val(x), next(nullptr) {}
      ListNode(int x, ListNode *next) : val(x), next(next) {}
  };
 
class Solution {
public:
    ListNode* trainningPlan(ListNode* head) {
        ListNode* cur = head, * prev = nullptr;
        if (!cur)return head;
        ListNode* Next = cur->next;
        while (cur && Next) {
            cur->next = prev;
            prev = cur;
            cur = Next;
            Next = cur->next;
        }
        cur->next = prev;
        return cur;
    }
};